1. Field of the Invention
This invention relates to a heavy duty pneumatic radial tire, and more particularly to a heavy duty pneumatic radial tire comprising a radial carcass of a rubberized cord ply extending between a pair of bead cores and turned around each bead core from inside of the tire toward outside thereof. A belt is superimposed about a crown portion of the carcass on an outer peripheral surface thereof and comprised of a main cross belt and a tread portion, in which the main cross belt is formed by laminating at least three rubberized cord layers each containing a plurality of substantially inextensible metal cords therein so that the cords in each layer are parallel to each other but the cords between the adjoining layers are crossed with each other and extend in opposite directions with respect to an equatorial line of the tire.
2. Description of Related Art
In general, it is apt to cause separation failure at belt end in the heavy duty pneumatic tires representing a pneumatic tire for construction vehicle provided with the main cross belt as mentioned above. This separation failure at belt end is caused by rubber fatigue at the belt end due to interlaminar shearing strain based on an air pressure of the tire and dynamic interlaminar shearing strain applied by load applied to the tire, driving force, braking force, lateral force and the like.
In order to prevent such a belt end separation failure, in the conventional heavy duty pneumatic radial tire having the main cross belt, a pair of cushion rubbers are arranged at both belt ends to cover both end portions of rubberized cord layers between adjoining cord layers forming the main cross belt, but special consideration is not made with respect to a position relation between the mutual cushion rubbers at both belt ends. As a result, the shearing strain between the rubberized cord layer constituting the main cross belt and the cushion rubber at the belt end is rather increased and there may frequently be caused an inconvenience of facilitating the occurrence of the belt end separation failure.